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First published online 16 August 2005
doi: 10.1242/jcs.02520

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Evidence for the presence of a low-mass ß1 integrin on the cell surface

¹ Manitoba Centre for Proteomics and Systems Biology, Department of Internal Medicine, University of Manitoba, 715 McDermot Avenue, Winnipeg, MB, Canada R3E 3P4
² Rheumatic Diseases Research Laboratory, Department of Internal Medicine, University of Manitoba, 715 McDermot Avenue, Winnipeg, MB, Canada R3E 3P4
³ Time of Flight Laboratory, Department of Physics and Astronomy, University of Manitoba, Winnipeg, MB, Canada R3T 2N2
⁴ The Wellcome Trust Centre for Cell-Matrix Research, School of Biological Sciences, University of Manchester, Oxford Road, Manchester M13 9PT, UK

^* Author for correspondence (e-mail: jwilkin{at}cc.umanitoba.ca)

Accepted 6 June 2005

Although the cell line K562 reportedly expresses a single species of ß1 integrin, 5ß1, surface staining with monoclonal antibodies JB1A, 12G10 and B3B11 to the ß1 chain clearly demonstrated differences in the expression levels of the epitopes detected by these antibodies. The present studies were initiated to determine the basis for this molecular heterogeneity in the integrins. Cross-linking of surface integrins with B3B11 caused their selective aggregation. This distribution was similar to that observed for the 5 chain. In contrast, cross-linking the ß1 chains with 12G10 did not cause codistribution of 5, suggesting that these two species were not associated on the cell surface. Immunoprecipitates of the surface integrins of K562 cells indicated the presence of 120 and 140 kDa forms of the ß1 chain which were detected by 12G10 and B3B11, respectively. Immunological, biochemical and mass spectrometric analysis of K562 surface integrins also failed to demonstrate the presence of any chain in association with the 120 kDa species of ß1 of K562 cells. Treatment of the two forms of ß1 with PGNase reduced their masses to 90 kDa, suggesting that N-glycosylation was responsible for the mass differences. Collectively, these results provide evidence for a novel species of ß1 on the cell surface, which does not appear to be associated with any chain. The data also suggest that differences in glycosylation may be involved in defining the association between the integrin and ß chains and the functional properties of these integrins.

Key words: ß1 integrin, 12G10, Glycosylation, Monomer, Mass spectrometry